I don't know if this has been mentioned before but I'm going to post it anyway and I'm sorry for not searching but this is a one off post and I want to start playing the game as soon as.
Some things I've found out about the key:
1.) You can type a key longer than the number of spaces and if theres a space afterwards it doesn't seem to work.
2.) I pressed Caps Lock on my keyboard and it registered it as a "letter" (grey box) in the space for the key. I don't know if pressing Return etc has the same effect or not.
3.) If you are having key troubles I'd try re-starting the game and in my case the first letter of the key magically appeared.

So it looks like the key isn't being trimmed properly or the key is case sensitive, and the input from the keyboard is a bit sloppy.
Hope it helps somebody out there...

I don't suppose there's a way to transfer my retail box Defcon key to Steam? I recently bought the Orange Box and have instantly fallen in love with the idea that, if I lose my CD and key, all I have to do is log into my Steam account and hit download. It's nice to have all my games in the same place too.

If I can also get it with Darwinia and Uplink, that would be even better.